I have never been very successfull locating swordfish. I think I have read most commonly available threads on this subject. For some reason, I have not been able to reduce the definitions to a visual search algorithm. I visit Brainbashers frequently and many of their superhard puzzles contain swordfish, forcing me to peak at the step by step solution. I would appreciate any help you folks can offer.

That is a good question because I never associated size and shape as a pair. Initially its basic swordfish growing to Franken, and others perhaps. I have come across the terms you presented but never gave them much consideration. Some examples would help me if you would be so kind and exactly how would you logically search rows and columns to identify the pattern. The one I have not heard of is the 1-fish.

The 1-fish is there for "completeness". It's equivalent to a Hidden Single.

Describing how to find a "basic" Swordfish is relatively easy. However, they are, IMO, less common than "finned" and "Sashimi" Swordfish, which are more difficult to find. The remaining shapes get successively more difficult to find, IMO.

[Withdrawn: I'm not really prepared to provide examples.]

Last edited by daj95376 on Sat Aug 20, 2011 1:50 am; edited 1 time in total

Marty, I agree with your after-basics code, which I found to be quite challenging. Will try to get the code into some type of solver that facilitates searching for fish one number at a time. Any suggestions here?

What is the definition of an S-Wing? It looks like you used the same candidate to follow two different paths that reached the same conclusion.

There are two, almost identical, S-Wings for the same elimination. I listed both.

There are several common patterns that involve three strong links using only two values -- W-Wing, M-Wing, S-Wing, and L2-Wing. It adds content to an AIC when it's identified as following one of these patterns.

I believe there is a thread in the Techniques forum showing S-Wing pattern configurations.

my solver treats things such as 'the possible placements of digit 7 in column 4'
the same way as 'the possible values of cell (3,5)'.

This means that matched pairs is treated the same as X-wings.
For example, an X-wings in my solver gives the output:

Code:

Must have number 9 at (1,5) (and number 9 at (9,8))
or number 9 at (9,5) (and number 9 at (1,8))
reducing options for digit 9 in column 5
Must have number 9 at (1,8) (and number 9 at (9,5))
or number 9 at (9,8) (and number 9 at (1,5))
reducing options for digit 9 in column 8

and a matched pair gives the output:

Code:

Must have number 2 at (1,2) (and number 3 at (1,9))
or number 2 at (1,9) (and number 3 at (1,2))
reducing options for digit 2 in row 1
Must have number 3 at (1,2) (and number 2 at (1,9))
or number 3 at (1,9) (and number 2 at (1,2))
reducing options for digit 3 in row 1

In the same way (if I had implemented them)
a matched triplet would be equivalent to Swordfish,
a matched quadruplet equivalent to Jellyfish,
etc.

Marty & Keith, I'm glad I'm not the only person who dislikes complex swordfish patterns - I thought I was a bit wimpish. Soon after the sudoku craze started (04, 05?) I was given a book of puzzles but it was so riddled with swordfish (which I couldn't see without writing in candidates) that I just gave up on sudokus.

Still, any port in a storm as they say, and I do look for swordfish if all else fails. (But not variants, which I've never found.) I'm about to post a puzzle that I just couldn't unlock without a swordfish.